Study on temperature calibration of a silicon substrate in a temperature
programmed desorption analysis
N. Hirashita,a) T. Jimbo,b) T. Matsunaga,c) M. Matsuura,d) M. Morita,e) I. Nishiyama,f) M.
Nishizuka,g) H. Okumura,h) A. Shimazaki,i) and N. Yabumotoj)
Working Group of Equipment, Ultraclean Standardization Committee, Ultraclean Society, Cosmos Hongo,
Building 8F, 4-1-4 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
共Received 11 September 2000; accepted 30 April 2001兲
In this work we propose a standard practice covering temperature calibration of a Si substrate,
ranging from 400 to 1000 °C, for temperature programmed desorption 共TPD兲 analysis. The practice
consists of heating silicon calibration materials at a controlled rate in a TPD instrument, measuring
characteristic desorption peak temperatures, and quadratic calibration fitting the measured
temperatures to standard temperatures. The calibration materials are 共1兲 a CaC2O4•H2O pellet on Si,
共2兲 Ar, and 共3兲 H ion implanted into Si wafers. The standard temperatures of the characteristic
desorption, associated with decomposition, structural transformation, and lamination of Si, were
determined by a special TPD instrument with the highest isothermal space around the specimen in
several laboratories, which was confirmed to be accurate for practical application. The precision of
this practice was determined in an interlaboratory test in which four to five laboratories participated
using two different instrumental models. This proved that the correction practice provided
interlaboratory precision of 5.7 °C between 400 and 1000 °C for ramping rates of 10, 30, and
60 °C/min. © 2001 American Vacuum Society. 关DOI: 10.1116/1.1380231兴
I. INTRODUCTION
Over the past decade, thermally evolved gas analysis, socalled temperature programmed desorption 共TPD兲 or thermal
desorption spectroscopy 共TDS兲, has been widely used in the
research and development of fabrication processes and in
new material used in ultralarge-scale integrated 共ULSI兲
circuits.1 This is because of the high detection sensitivity of
thermal desorption and high reproducibility of evaluation
even for air components such as H2 and H2O. 2 The outgassing characteristics of Si substrates as well as of thin film
used in ULSI devices, such as desorption temperature, the
amount of outgassing, and assignment of outgasing molecules, are important for developing device reliability3,4 and
can be most conveniently determined by this method.
In thermal analyses which employ temperature scanning
at a constant heating rate, the temperature of the specimen
rises as a result of heat flow from the heat source. This inevitably creates a temperature gradient between the specimen
and the temperature-measuring device. Since, in particular,
TPD measurements in a high vacuum generally make it difficult to secure reasonable isothermal space, the temperaturea兲
Present address: Oki Electric Industry Co. Ltd.; electronic mail:
[email protected]
b兲
Present address: Hitachi, Ltd.
c兲
Present address: Matsushita Technoresearch, Inc.; electronic mail:
[email protected]
d兲
Present address: Mitsubishi Electric Corporation.
e兲
Present address: Osaka University.
f兲
Present address: NEC Corporation.
g兲
Present address: Toshiba Microelectronics Corporation.
h兲
Present address: Toray Research Center, Inc.
i兲
Present address: Toshiba Corporation.
j兲
Present address: NTT Advanced Technology Corporation; electronic mail:
[email protected]
1255
J. Vac. Sci. Technol. A 19„4…, JulÕAug 2001
measuring device, if inadequately positioned, may not indicate the exact temperature of the specimen. However, the
instrument’s ramping temperature was not precisely calibrated to the specimen temperature in most instruments due
to difficulties in measuring the specimen temperature in
vacuum. These circumstances used to provide rather large
differences in desorption temperature between one laboratory
and another.
In order to assess the temperature discrepancy in TPD
measurements and, if necessary, to establish a standard
method by which to correct specimen temperature of the Si
substrate, the Working Group of Equipment started research
as part as the Ultraclean Standardization Committee of the
Ultraclean Society in 1996. The Group involved 10 organizations 共9 private enterprises made up of 7 ULSI device
manufacturers and a university兲 with three kinds of instrument model of the TPD apparatus. According to the standard
procedure5,6 used in thermal analysis, we started to find sublimation, melting transition, phase transformation materials
rather than pyrolytic surface desorption materials as
temperature-calibration standards. However, there has been
little work on this issue, since desorption concomitant with
the phase transformation is necessary for TPD measurements. In this regard, nevertheless, organic solvents included
in inorganic crystal complexes such as in 1, 4-dioxane including K2SO4 have been reported to evolve during crystalline phase transformation of the matrix.7 Also, the decomposition temperature of CaC2O4 to evolve CO, leaving CaCO3,
had been reported to be less pressure dependent.8 In addition
to these kinds of inorganic complexes, ion-implanted Si materials have been also examined for temperature-calibration
standards because of their practical use in the semiconductor
industry.
0734-2101Õ2001Õ19„4…Õ1255Õ6Õ$18.00
©2001 American Vacuum Society
1255
1256
Hirashita et al.: Study on temperature calibration of silicon
1256
substrates using standard materials for TPD analysis, with
temperatures ranging from 400 to 1000 °C.
II. EXPERIMENT
FIG. 1. Schematics of three instrument models of TPD apparatuses used in
this work.
The Working Group found that even using the same materials the desorption temperature differed more than 100 °C
between different laboratories. In this article we propose a
standard practice covering temperature calibration of silicon
Three instrument models of the TPD apparatus were used
in this work of the Working Group, and they are schematically shown in Fig. 1. Types 共a兲 and 共b兲 used an infrared
light for specimen heating while, in type 共c兲, the specimen
was heated in a Ta crucible furnace by W resistive heating.
The base pressures of all apparatuses were less than 10⫺4 Pa
and the apparatuses equipped with a quadrupole mass spectrometer for desorbed gas measurements. Type 共a兲 was also
equipped with a loadlock chamber for easy specimen exchange.
In type 共a兲, the specimen temperature was measured by
two methods. The first method used a W/Re thermocouple
共0.25 mm in diameter兲 placed in the specimen stage of quartz
just below the specimen 共⬍0.5 mm兲, as shown in Fig. 1共a兲.
The other was measured by a W/Re thermocouple 共0.1 mm
in diameter兲 attached to the specimen surface using a linear
motion feedthrough unit in vacuum. Ramp heating of specimen could be controlled by either device. In type 共b兲, the
specimen temperature was measured by a type R thermocouple placed in the neighborhood of the specimen. Both
were placed in a uniform temperature region of the furnace.
In type 共c兲, a Ta crucible was placed on a Ta plate, with the
type R thermocouple being caulked, and was immersed in a
W resistive heating furnace, as described later in detail.
Ramping rates of 10, 30, and 60 °C/min were examined in
this work for practical application.
Various materials with H and Ar ion-implanted Si wafers
and pellets of inorganic complexes on Si, such as oxalate
共CaC2O4 and BaC2O4兲, sulfate 共K2SO4 and ZnSO4兲, carbonate 共Na2CO3, CaCO3, BaCO3, and SrCO3兲, and nitrate
(NaNO3), were examined by TPD analysis in different laboratories.
In some TPD apparatuses, the ramping temperature was
calibrated to the Si temperature by a special thermocouple
embedded with ceramics in Si wafers.9 The applicability of
this calibration method was also examined by measuring the
same specimens in each laboratory. It should be noted that an
absolute temperature accuracy of ⫾0.5% was guaranteed for
all thermocouples used in this work.
TABLE I. Material used to examine the Si specimen temperature.
Specimen
Specification
A
B
H⫹ implanted Si 共with 40 kV/1⫻1017 cm⫺2)
CaC2O4H2O pellet on Si
C
D
E
Ar⫹ implanted Si 共with 60 kV/2⫻1015 cm⫺2兲
15
⫺2
BF⫹
2 implanted Si 共with 60 kV/5⫻10 cm 兲
H-terminated Si共100兲 surface
J. Vac. Sci. Technol. A, Vol. 19, No. 4, JulÕAug 2001
Desorption
共°C兲
H2 共⬃400兲
Co 共⬃520兲
CO2 共⬃600兲
Ar 共⬃700 and ⬃1000兲
SiF4 共⬃670兲
H2 共⬃400 and ⬃500兲
1257
Hirashita et al.: Study on temperature calibration of silicon
FIG. 2. Desorption curves obtained from the standard specimens. Desorption
curve 共a兲 is a pyrograph of a mass number of 2 from standard specimen A.
Desorption curve 共b兲 is a pyrograph of a mass number of 28 from standard
specimen B. Desorption curve 共c兲 is a pyrograph of a mass number of 40
from standard specimen C.
III. RESULTS AND DISCUSSION
Ion-implanted specimens demonstrated distinct sharp desorption characteristics and high reproducibility, while inorJVST A - Vacuum, Surfaces, and Films
1257
ganic complexes other than oxalate did not exhibit any reproducible desorption characteristics. Possible materials for
examining the Si specimen temperature are determined by
the following criteria: easy measurement 共showing a sharp
desorption peak兲, no history of specimen preparation, stability, and easy availability. The most plausible candidates are
listed in Table I as well as specimen preparation. Details of
the preparation are described in the Appendix.
Typical desorption curves obtained from the specimens of
A, B, and C in Table I are shown in Fig. 2. Desorption curve
共a兲 is a pyrograph of H2 from specimen A 共H⫹ implanted Si兲.
Desorption curve 共b兲 is a pyrograph of CO from specimen B
共CaC2O4•H2O pellet on Si兲. Desorption curve 共c兲 is a pyrograph of Ar from specimen C 共Ar⫹ implanted Si兲. We refer
to the desorption peaks as A 1 , B 1 , C 1 , and C 2 , denoted in
Fig. 2. The A 1 desorption is considered to be attributed to
lamination of the Si films due to cleavage.10 The B 1 desorption results from the decomposition of CaC2O4 to form
CaCO3. The C 1 desorption is associated with the solid phase
epitaxial growth of amorphous Si formed by ion implantation and the C 2 desorption with the epitaxial realignment of
microcrystalline Si.11 Since all exhibit fairly sharp desorption
peaks, the desorption temperature is defined as the temperature at the top of the desorption peak.
The desorption temperatures of A 1 , B 1 , C 1 , and C 2
peaks measured at different laboratories are listed in Table II,
which shows that the desorption temperatures differed more
than 100 °C between laboratories. The ramping rate was
30 °C/min. Also tabulated are desorption temperatures measured after each instrumental ramping temperature calibrated
to the Si temperature using the thermocouple embedded with
ceramics in the Si specimen. However, the results between
interlaboratory tests are varied, indicating the need for a standard practice for temperature correction of Si substrates using a standard specimen for TPD analysis.
The temperature calibration method proposed in this work
consists of measuring standard specimens to find the desorption peak temperatures for individual instruments and subsequent correction of the instruments’ ramping temperature by
means of a quadratic function fitting the measured temperatures to the standard desorption temperatures. Therefore, the
silicon substrate temperature can be obtained by quadratic
fitting as a function of the instrument’s ramping temperature
for a certain ramping rate. According to the criteria previously mentioned we selected specimens A, B, and C in Table
I as temperature-calibration standard specimens. The quadratic function fitting was found to provide a better fit than
linear fitting for all types of TPD apparatus. The applicability
of this correction practice is discussed next.
Standard desorption temperatures were first determined
by a TPD apparatus of type 共c兲 which had the highest isothermal space around the specimen among others in our
Working Group. A schematic showing instrument details is
in Fig. 3. Standard specimens were mounted on Si substrates,
in which the type R thermocouple was embedded with ceramics, and were inserted into the crucible, and ramping was
controlled by the embedded thermocouple. Standard desorp-
1258
Hirashita et al.: Study on temperature calibration of silicon
1258
TABLE II. Desorption peak temperatures 共°C兲 from specimens of A, B, and C in Table I before and after
temperature calibration using thermocouples embedded in a Si substrate.
Organization 共TPD type兲
Before
calibration
After
calibration
Desorption
1共a兲
2共b兲
3共c兲
4共a兲
5共a兲
Average
Standard
deviation
A1
¯
¯
¯
¯
¯
¯
¯
B1
C1
C2
502
792
1173
525
680
990
549
746
1153
468
675
981
556
718
1078
520
722.2
1075
36.0
48.6
89.1
A1
408
¯
413
¯
¯
410.5
3.5
B1
C1
C2
533
711
1008
543
715
998
530
706
973
529
708
1019
532
686
961
533.4
705.2
991.8
5.6
11.3
24.2
TABLE III. Desorption peak temperature 共°C兲 of the standard materials.
Standard specimen C
Ar⫹ implanted Si
(2⫻1015/cm2) substrate
Ramping
rate
共°C/min兲
Standard specimen A
H⫹ implanted Si
(1⫻1017/cm2) substrate
Peak A 1
Standard specimen B
CaC2O4•H2O pellet
on a Si substrate
Peak B 1
Peak C 1
Peak C 2
10
30
60
374
396
420
511
522
533
681
706
720
959
988
1003
TABLE IV. Desorption peak temperatures 共°C兲 of the standard materials obtained by various methods. A
ramping rate of 30 °C/min was used for all measurements.
Ramping
rate
共30 °C/min兲
Method
Standard specimen C
Ar⫹ implanted Si
(2⫻1015/cm2) substrate
Standard specimen A
H⫹ implanted Si
(1⫻1017/cm2) substrate
Peak A 1
Standard specimen B
CaC2O4•H2O pellet
on a Si substrate
Peak B 1
Peak C 1
Peak C 2
396⫾1
398⫾2
¯
¯
522
529⫾6
¯
524
706⫾1
707⫾5
724
¯
988
998⫾9
¯
¯
This work
Embedded TC
TG-MS
TG
TABLE V. Summary of interlaboratory testing using specimens B, D, and E in Table I. The unit of measure is °C.
Ramping
共°C兲 rate
Organization 共TPD type兲
Specimen
1共a兲
2共b兲
3共a兲
4共a兲
5共a兲
Average
Standard
deviation
10
E
E
B
D
358
486
571
644
357
502
582
630
340
493
570
636
362
495
573
646
¯
¯
¯
¯
354.3
494.0
574.0
639.0
9.7
6.6
5.5
7.4
30
E
E
B
D
370
506
595
666
381
512
594
680
351
508
585
663
367
506
598
676
379
507
606
667
367.3
508.0
593.0
671.3
12.4
2.8
5.6
8.1
60
E
E
B
D
404
522
615
682
408
543
618
679
419
527
604
673
401
531
617
679
405
523
609
677
408.0
530.8
613.5
678.3
7.9
9.0
6.5
3.8
J. Vac. Sci. Technol. A, Vol. 19, No. 4, JulÕAug 2001
1259
Hirashita et al.: Study on temperature calibration of silicon
FIG. 3. Schematic drawing of measurement of the standard temperatures.
tion temperatures of A 1 , B 1 , C 1 , and C 2 peaks measured by
this method are summarized in Table III for ramping rates of
10, 30, and 60 °C/min. These desorption temperatures were
precisely reproduced within ⫾1 °C over a few measurements.
Table IV compares desorption peak temperatures measured by this method with other methods such as thermogravimetry 共TG兲 and thermogravimetry-mass spectrometry
共TG-MS兲 measurements with the same ramping rate of
30 °C/min. Specimen temperatures of TG and TG-MS measurements were calibrated by the standard method.5,6 Also,
the desorption temperatures evaluated by all instrument models, where ramping was controlled by the thermocouple embedded in the standard specimens, agree well each other and
the average values are given in Table IV. The measurements
by each technique are found to agree well, although the TG
and TG-MS measurements were employed at atmospheric
pressure. As previously mentioned, the C 1 desorption is concomitant with the solid phase epitaxial growth of amorphous
Si formed by ion implantation, which does not involve a
significant volume change. Thus, thermodynamical consideration, known as the Clausius–Clapeyron relationship, predicts that the phase transformation temperature is less pressure dependent. It is also noted that although the B 1
desorption is associated with the decomposition of CaC2O4,
the desorption temperature is found to be less pressure dependent, as evidenced by a fact that the CO desorption temperature is coincident between TG, reduced pressure TG, and
TPD measurements.12 Similar results had been reported for
that system.8 Therefore, the validity of the standard temperatures measured by the aforementioned method using type 共c兲
is considered to be assured.
The precision of this method was determined in an interlaboratory test in which five laboratories participated using
two instrument models other than the type 共c兲 used to determine the standard desorption temperatures. In this test, the
common specimens of B 共CaC2O4 •H2O pellet on Si兲, D
(BF⫹
2 implanted Si兲, and E 关H-terminated Si共100兲 surface兴 in
JVST A - Vacuum, Surfaces, and Films
1259
FIG. 4. Relationship between standard deviation and average desorption
peak temperature of common specimens obtained from interlaboratory tests.
Table I were used to measure desorption of CO2, SiF4, and
H2, each for 10, 30, and 60 °C/min. The measured results are
summarized in Table V. The desorption temperatures corrected by this practice agree fairly well among laboratories.
The standard deviation of the corrected desorption temperatures is also plotted in Fig. 4 as a function of the average of
the corrected temperature, where the average temperature below 400 °C was removed because of less reliable data due to
extrapolation of the fitting procedure. All standard deviation
is found to be below 10 °C. The results are, however, scattered and do not show any schematic dependence on temperature. The normalized standard deviation, evaluated from
all deviations from the average values for each interlaboratory test condition, was approximately 5.7 °C. Consequently,
the normalized standard deviation of 5.7 °C is considered to
be applicable to the precision of the Si substrate temperature
throughout the temperature range of 400–1000 °C by this
practice.
Finally, a prescription of the standard specimens should
be discussed. The ion-implanted Si specimens were stable
and time-dependent deterioration was not evident over several years during the course of this study. However, ionimplantation conditions, such as a dose in quantity and acceleration energy, were found to alter the desorption
characteristics. The ion implantation calibrated within 5%
accuracy is recommended for use in the standard specimen
preparation. Also, 6 and 8 in. wafers are confirmed to provide the same temperature. The standard specimen of a
CaC2O4 •H2O pellet on Si was also rather stable and timedependent deterioration was not evident over a period of a
few weeks. Although the details are not clarified yet, the
temperature of the B 1 desorption was not dependent on the
amount of CaC2O4 •H2O pellet on Si within a range in quantity, as described in the Appendix.
IV. CONCLUSION
A standard practice covering temperature calibration of a
silicon substrate, ranging from 400 to 1000 °C, for tempera-
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Hirashita et al.: Study on temperature calibration of silicon
ture programmed desorption analysis was proposed. The
practice consists of heating silicon calibration materials at a
controlled rate in a TPD instrument, measuring characteristic
desorption peak temperatures, and quadratic calibration fitting of these results to the standard temperatures. The calibration materials are a CaC2O4 •H2O pellet on Si, Ar, and H
ion implanted into Si wafers. The standard temperatures of
the characteristic desorption, associated with decomposition,
structural transformation and lamination of silicon, were determined by a special TPD instrument with the highest isothermal space around the specimen among the laboratories.
The precision of this practice was examined by an interlaboratory test in which four to five laboratories participated using two different instrument models. This test using a few
common specimens proves that the normalized standard deviation, measured in different laboratories for all the measurements with ramping rates of 10, 30, and 60 °C/min, is
estimated to be 5.7 °C between 400 and 1000 °C.
ACKNOWLEDGMENTS
The authors would like to thank Professor Takeo Ozawa
of Chiba Institute of Technology, Professor Tadahiro Ohmi
of Tohoku University, Professor Yasuo Tarui of Waseda
University, and Dr. Hiroyuki Harada of Nisso Engineering
Co. for discussion and encouragement. They also deeply
thank Dr. Tsuneo Ajioka of NTT Electronics, Dr. Ken-ichi
Ohtsuka and Dr. Takaaki Kimura of Fujitsu, Dr. Hidehiro
Kojiri of Applied Matrials Japan, Dr. Hideki Tomioka of
Hitachi, Dr. Yoshikatsu Nagasawa of Toray Research Center, and Dr. Yoshiaki Yoshioka of Matsushita Technoresearch, who offered many ideas and data as members for
some of the duration of the research activity of the Working
Group of Equipment, Ultraclean Society.
APPENDIX: SPECIMEN PREPARATION
1. H¿ implanted Si „high dose…
A Czochralski-grown 共Cz兲 p-type 共1–2 ⍀ cm兲 Si 共100兲
wafer 6 or 8 in. in diameter was first oxidized to 10 nm
thickness. H⫹ was implanted into Si through the oxide at an
acceleration energy of 40 kV with a dose of 1⫻1017/cm2 and
an incident angle of 7°. A significant increase in wafer temperature during ion implantation was avoided by the use of
ion current of ⬍10 mA and/or with the wafers being
mounted on a water-cooled disk. The surface oxide was not
removed before TPD measurements.
2. CaC2O4"H2O pellet on Si
Commercially available CaC2O4•H2O 0.5 g in weight was
added into 10 ml of de-ionized water and agitated well at
room temperature. A suspension of 5–10 ␮l was dropped
onto the Cz Si 共100兲 surface and dried at atmospheric pressure to a form pellet.
J. Vac. Sci. Technol. A, Vol. 19, No. 4, JulÕAug 2001
1260
3. Ar¿ implanted Si
A Cz p-type 共2–5 ⍀ cm兲 Si 共100兲 wafer 6 or 8 in. in
diameter was first oxidized to 2 nm thickness. Ar⫹ was implanted into Si through the oxide at an acceleration energy of
60 kV with a dose of 2⫻1015/cm2 and an incident angle of
7°. A significant increase in wafer temperature during ion
implantation was avoided by the use of an ion current of
⬍10 mA and/or with the wafers being mounted on a watercooled disk. The surface oxide was not removed before TPD
measurements.
4. BF2¿ implanted Si
A Cz n-type 共10–20 ⍀ cm兲 Si 共100兲 wafer of 6 or 8 in. in
diameter was first oxidized to 10 nm thickness. BF⫹
2 was
implanted into Si through the oxide at an acceleration energy
of 60 kV with a dose of 5⫻1015/cm2 and an incident angle
of 7°. A significant increase in wafer temperature during ion
implantation was avoided by the use of an ion current of
⬍10 mA and/or with the wafers being mounted on a watercooled disk. The surface oxide should be removed by dilute
HF solution prior to TPD measurements.
5. H-terminated Si „100… surface
A chemically cleaned Cz p-type 共1–10 ⍀ cm兲 Si 共100兲
substrate was dipped into 0.5%–5% HF solution, rinsed by
de-ionized water, and dried to form H-terminated Si
surfaces.13
1
N. Yabumoto, K. Minegishi, K. Saito, M. Morita, and T. Ohmi, Proceedings of the 1st International Symposium on Cleaning Technology in Semiconductor Device Manufacturing/1989, edited by J. Ruzyllo and R. E.
Novak 共The Electrochemical Society, Pennington, NJ, 1990兲, Vol. 90–9,
p. 265.
2
N. Hirashita and T. Uchiyama, Bunseki Kagaku 43, 757 共1994兲.
3
N. Shimoyama, K. Machida, K. Naruse, and T. Tsuchiya, VLSI Tech.
Dig. 94 共1992兲; K. Shimokawa, T. Usami, S. Tokitoh, N. Hirashita, M.
Yoshimaru, and M. Ino, ibid. 96 共1992兲.
4
N. Hirashita, M. Kobayakawa, A. Arimatsu, F. Yokoyama, and T. Ajioka,
J. Electrochem. Soc. 139, 794 共1992兲; N. Hirashita, S. Tokitoh, and H.
Uchida, Jpn. J. Appl. Phys., Part 1 32, 1787 共1993兲.
5
JIS K0129, Japanese Industrial Standard General Rules for Thermal
Analysis 共1994兲.
6
ASTM E967-83 共1984兲, pp. 815–820.
7
P. D. Gam and R. L. Tucker, J. Therm. Anal. 5, 483 共1973兲.
8
K. P. Pribylov, D. Sh. Fazlullina, and R. M. Chechetkin, J. Inorg. Chem.
8, 3182 共1968兲.
9
P. Vandenabeele and W. Renken, Mater. Res. Soc. Symp. Proc. 470, 17
共1997兲.
10
Q.-Y. Tong and R. W. Bower, MRS Bull. 40 共1998兲.
11
N. Hirashita, Jpn. J. Appl. Phys., Part 1 38, 613 共1999兲.
12
T. Matsunaga 共private communication兲.
13
T. Takahagi, I. Nagai, A. Ishitani, H. Kuroda, and N. Nagasawa, J. Appl.
Phys. 64, 3516 共1988兲.